Structural analysis of hydroperoxides formed by oxidation of phosphatidylcholine with singlet oxygen

Abstract

Abstract Soybean phosphatidylcholine (PC) and dilinoleoyl PC (di‐18∶2 PC) were oxidized with singlet molecular oxygen using methylene blue as the photosensitizer. The oxidation products, PC monohydroperoxides (PC‐MHP) and PC dihydroperoxides (PC‐DHP), were isolated by reverse phase liquid chromatography, and their structures were analyzed by nuclear magnetic resonance (NMR) and gas chromatography‐mass spectrometry (GC‐MS). Signals for the hydroperoxy proton appeared downfield in NMR spectra of PC‐MHP and PC‐DHP. Soybean PC‐MHP and di‐18∶2 PC‐MHP were converted to trimethylsilyl (TMS) derivatives of hydrogenated diglycerides when treated with phospholipase C and hydrogenated. The tert ‐butyldimethylsilyl (TBDMS) derivatives of hydrogenated diglycerides were also prepared from di‐18∶2 PC‐MHP. Fragmentation of the TMS and TBDMS derivatives was obtained in electron impact mass spectra. The isomeric composition of hydroperoxylinoleate component in di‐18∶2 PC‐MHP was determined by methanolysis of the hydrogenated diglyceride and mass chromatographic analysis of the resulting isomeric hydroxy octadecanoates.